The present invention relates to a device and a method for determining a roadway gradient quantity.
Conventional gradient sensors have different designs and different modes of operation. For example, U.S. Pat. Nos. 4,779,353, 5,428,902, and German Patent No. DE 40 25 184 describe gradient sensors having a sensor body which is filled with a measuring liquid whose liquid level aligns in response to an inclination. From the position of the liquid level, it is then possible to determine the inclination of a motor vehicle. The position of the liquid level is ascertained either on the basis of a change in resistance or a change in capacitance. Both the change in resistance and the change in capacitance are produced by the change in position of the liquid level of the measuring liquid and the associated different wetting of electrodes which are located in the sensor body.
Gradient sensors of the kind described above have the disadvantage of a complex design, resulting in their susceptibility to faults. This can lead to an increased risk of failure, therefore they are not possible for permanent use in a motor vehicle.
Other conventional sensors operate in accordance with the principle that an acceleration acting upon the sensor is converted into a change in pressure which is used as a measure for the acceleration acting upon the sensor. U.S. Pat. No. 3,046,793 describes an acceleration sensor having a cylindrical sensor body which is filled with a measuring liquid. The measuring liquid is used for damping the moving parts of the acceleration sensor and for converting an acceleration into a pressure. This pressure is measured and the acceleration is determined from the change in pressure. U.S. Pat. No. 5,291,784 describes an acceleration sensor having a cylindrical sensor body which is divided into two measuring chambers by a membrane. The measuring chambers are filled with a measuring liquid. An acceleration results in a pressure difference between the two measuring chambers. This pressure difference is measured, and the acceleration is determined therefrom.
The two aforementioned types of acceleration sensors are not suitable for determining the roadway gradient of a motor vehicle. They measure a pressure which develops because an acceleration acts upon the measuring liquid in the sensors. Since they contain moving parts, they are susceptible to faults.
Additionally, liquid level indicators which are used in vehicles. European Patent No. EP 0 303 874 describes a device for ascertaining the liquid quantity in a fuel tank which is mounted in a vehicle. The device includes three level sensors which are arranged in a predetermined position relative to each other. On the basis of the measured values of the three level sensors, a value for the filling amount of the tank, and a value for the inclination of the tank, and, consequently, also of the vehicle is calculated. When ascertaining the filling amount, the inclination of the tank is taken into account. Therefore, the ascertained filling amount is independent of either the inclination of the tank or of the vehicle.
German Patent No. DE 197 04 683 describes a device for measuring the inclination of a container relative to a liquid level inside the tank. In the case of a rigid installation of the container in the vehicle, it is possible to infer the vehicle inclination and the vehicle acceleration. According to an exemplary embodiment, three sensors are used for ascertaining the inclination of the container or of the vehicle. An inclination of the container results in different liquid levels; consequently, the sensors give out different voltages accordingly. On the basis of the different voltages and the known geometric arrangement of the liquid level sensors, a gradient signal is determined with the assistance of an evaluation circuit.
Using the two last-mentioned devices, it is possible to ascertain the inclination of the liquid container, and, consequently, also that of the vehicle. The gradient of the roadway on which the vehicle stands or moves, in the following also called roadway gradient or slope gradient, cannot be ascertained by any of the two aforementioned devices for the following reason: if one wishes to ascertain the roadway gradient on the basis of the inclination of the liquid container, then the motion of the vehicle must also be considered in doing so. The inclination of the vehicle is substantially composed of two components. One component originates from the gradient of the roadway. The other component results from the motion of the vehicle, as exists, for example, during acceleration or deceleration (pitching) or during a steering maneuver (rolling motion). Since, within the framework of determining the vehicle inclination when working with the two devices appertaining to the related art, no quantities are available which describe the aforementioned vehicle movement, the roadway gradient cannot be ascertained with the assistance of these devices, because the vehicle movement cannot be eliminated from the vehicle inclination.
Even if the two devices were modified to the effect that, by using them, it would be possible to ascertain the gradient of the roadway, they still have the disadvantage that they use liquid level indicators which contain moving parts, and therefore are susceptible to faults. Secondly, they require a non-negligible volume of liquid which is consequently lost from the tank capacity.
An object of the present invention is to provide a device for determining a roadway gradient quantity which has a rugged design, and which is reliable, i.e., little susceptibility to faults. Moreover, the measuring arrangement used should not require a lot of mounting volume.
In the case of a liquid container rigidly joined to the vehicle, the inclination of the liquid container corresponds to the inclination of the vehicle, or to the inclination of the liquid contained in the liquid container.
The device according to the present invention for determining a roadway gradient quantity, which describes the gradient of a roadway on which a vehicle is situated, includes a liquid container which is mounted to the vehicle and contains a liquid. In one advantageous embodiment, this liquid container is a fuel tank.
With regard to a rugged and reliable design of the device, an advantageous embodiment is the use of pressure sensors as a measuring arrangement. In this embodiment, at least one pressure sensor is mounted in the area of the bottom of the liquid container. Using this pressure sensor, a pressure quantity is ascertained which describes the hydrostatic pressure in the liquid container. The pressure sensor is in communication with an evaluation unit. In the evaluation unit, the roadway gradient quantity is determined as a function of the pressure quantity.
The roadway gradient quantity describes the roadway gradient along and/or transverse to the vehicle""s direction of travel.
In accordance with conventional physical principles, the evaluation unit determines the liquid level in the liquid container from the hydrostatic pressure and the inclination of the liquid container from the change in the liquid level, the inclination of the liquid container corresponding to the inclination of the vehicle. The roadway gradient quantity or slope gradient of the roadway surface is then determined from the inclination of the vehicle, taking into account vehicle movement. Herein the phrases xe2x80x9croadway gradient quantityxe2x80x9d and xe2x80x9cslope gradient of the roadwayxe2x80x9d are used interchangeably, and the phrases mean either a slope gradient of the roadway in the direction of travel of a vehicle or a slope gradient of the roadway transverse to the direction of travel of a vehicle or a combined vector of the slope gradient of the roadway both in the direction of travel and transverse to the direction of travel. The slope gradient is important information for recognizing the motor vehicle condition and for controlling specific motor vehicle functions. The slope gradient information is of significance, in particular in the detection of the mass of commercial vehicles, for coupling force control, and for vehicle dynamics control. Furthermore, it is possible to improve functions for engine timing (in gasoline and diesel engines), using the slope gradient information.
Using the device according to the present invention, it is possible to ascertain the roadway gradient in the direction of travel, or transverse to the direction of travel. The direction in which the roadway gradient can be determined depends on the number of pressure sensors and the positioning of the pressure sensors in the liquid container. As a general principle, the pressure sensors must not be mounted at a place on or in the liquid container where the liquid level does not change in response to changes in the roadway gradient.
The liquid level in the liquid container aligns according to the slope gradient, and the hydrostatic pressure at the pressure sensor changes with the slope gradient. This change is a measure for the instantaneous slope gradient of the entire vehicle. In this context, it is assumed that the gradient of the time rate of change of the liquid level resulting from the slope gradient is greater than the gradient of the time rate of change of the liquid level resulting from a current removal of liquid from the liquid container due to the operation of the motor vehicle. The gradients of the time rate of change of the liquid level are likewise calculated in the evaluation unit.
Suitable liquid containers include, for example, the container for the brake fluid, the container for the coolant, or the container for the windshield washer fluid. Important for selecting a suitable liquid container is that the specific liquid does not fill up the entire liquid container so that the liquid level can align relative to the liquid container in response to a sloped roadway surface. Ideally, the liquid container has a symmetrical cuboidal container geometry, and the liquid level should be able to align inside the liquid container in an unhindered manner, in accordance with the slope gradient. The mathematical relationships on the basis of which the roadway gradient is determined in the evaluation unit from the change in the liquid level are described in greater detail below for such a container geometry. For other container geometries, corresponding relationships to be individually determined can be ascertained (possibly also empirically). This applies also to liquid levels where the liquid level cannot freely align in accordance with the slope gradient.
In an advantageous embodiment, the liquid container is designed as a fuel tank. The fuel tank is usually the largest liquid container in a motor vehicle. Due to the size of the fuel tank, it is possible to arrange a plurality of pressure sensors at relatively great distances in relation to each other. When working with pressure sensors arranged at relatively great distances in relation to each other, the pressure differences measured in response to a vehicle inclination are greater than in the case of pressure sensors which are arranged close to each other. Because of the greater pressure differences, the accuracy of the device according to the present invention is increased.
In an advantageous embodiment of the present invention, the pressure sensors are incorporated in the bottom of the liquid container. In the case of a liquid container made of plastic, the pressure sensors can be directly cast and integrated with the plastic during the manufacture of the container. In this manner, efficient and inexpensive manufacturing of the device according to the present invention is possible. A further advantage of pressure sensors which are incorporated in the bottom of the liquid container is that the volume of the container is not reduced by the pressure sensors.
In an embodiment of the present invention, the accuracy and reliability of the device according to the present invention can be decisively improved by incorporating an arrangement for damping the sloshing motion of the liquid in the liquid container. This arrangement for damping the sloshing motion can be designed differently. In an advantageous embodiment, the arrangement for damping the sloshing motion is designed as a lining of porous material in the container or as platelike elements arranged inside the liquid container. These platelike elements can be designed, for example, as baffles. They can be arranged in the interior of the liquid container in nearly any way desired and, in particular, they can run parallel or orthogonally to each other.
According to the present invention, the hydrostatic pressure signal is evaluated as a function of the driving situation. The additional motion of the liquid in the liquid container during different driving situations can be analyzed beforehand either on the basis of road tests or by theoretical approaches. To take into account the driving situation in determining the roadway gradient quantity, at least one vehicle quantity which describes the vehicle motion and/or the vehicle condition is considered by the evaluation unit. To determine the vehicle quantity, the device according to the present invention makes provision for one or more detecting devices. These detecting devices include arrangements for detecting at least one of a value describing the vehicle""s acceleration, a value describing the vehicle""s steering angle, values describing the speeds of the individual wheels, a value describing the condition of the vehicle""s brakes, and a value describing the condition of the engine. T
he detecting arrangement for detecting a quantity describing the vehicle""s acceleration detect the acceleration in the direction of travel (i.e., a longitudinal acceleration) or transversely to the direction of travel (i.e. a transverse acceleration due to cornering or skidding motion of the motor vehicle). The longitudinal acceleration may be determined, for example, with the aid of the engine torque (fuel injection), or on the basis of the wheel speeds, which are measured with the assistance of wheel speed sensors. The transverse acceleration can be measured, for example, with the assistance of a transverse acceleration sensor. When determining the slope gradient in the evaluation unit, the vehicle acceleration is then considered in such a manner that the inclination of the liquid in the liquid container is corrected by the inclination value resulting from the acceleration. It is also possible, however, to completely prevent the inclination of the vehicle from being measured during the acceleration phase.
Alternatively or in addition to the vehicle""s acceleration, it is also possible to use the steering angle ascertained with the assistance of at least one of a steering angle sensor, the condition of the brakes, and the condition of the motor, to take into account the driving situation in determining the roadway gradient quantity in the evaluation unit. Information on the condition of the brakes can be provided, for example, by a brake slip control integrated in the vehicle. Accordingly, information on the condition of the motor can be provided by an ASR traction control system integrated in the vehicle.
The arrangement for ascertaining acceleration can also detect decelerations of the motor vehicle. The vehicle deceleration may also be taken account when determining the slope gradient. Alternatively, it is possible to evaluate brake pressure in order to measure vehicle deceleration.
If the roadway gradient is to be determined only in the direction of travel, the pressure sensor should ideally be mounted symmetrically to the width of the liquid container. For this purpose, the present invention proposes mounting a pressure sensor on the horizontal center line of the liquid container running in the direction of travel, at a distance from the vertical center line of the liquid container. This minimizes measuring influences transverse to the direction of travel due to the inclination of the vehicle, the slope gradient, or due to the vehicle""s acceleration or deceleration.
If the roadway gradient is to be determined only transversely to the direction of travel, the pressure sensor should ideally be mounted symmetrically to the length of the liquid container. For this purpose, the present invention proposes mounting a pressure sensor on the horizontal center line of the liquid container running transversely to the direction of travel, at a distance from the vertical center line of the liquid container. This minimizes measuring influences in the direction of travel due to the inclination of the vehicle, the slope gradient, or due to the vehicle""s acceleration or deceleration.
In the aforementioned embodiments where the present invention has only one pressure sensor, the pressure quantity values measured by the pressure sensor and present for successive time steps, are evaluated in the evaluation unit. For this purpose, two successive time steps are expediently examined. This procedure corresponds to a relative measurement, since, to determine the roadway gradient quantity, the time rate of change of the pressure quantity is required.
Also possible is an embodiment utilizing two pressure sensors, of which one pressure sensor determines slope gradients in the direction of travel and the other determines slope gradients transversely to the direction of travel. However, a device having two pressure sensors could also deliver absolute values for the inclination of the vehicle either in the direction of travel or transverse to the direction of travel.
An advantageous embodiment of the present invention proposes the mounting of two pressure sensors in the liquid container on the horizontal center line of the liquid container running in the direction of travel, at a distance from one another. Using such a sensor arrangement, it is possible to determine a slope gradient at any desired point of time. The pressure sensors are mounted symmetrically to the width of the liquid container. In this manner, inclinations can be determined only in the direction of travel. Measuring influences due to an inclination of the vehicle transverse to the direction of travel are reduced to a minimum. Instead of arranging the pressure sensors on the horizontal center line running transversely to the direction of travel, it would also be possible to arrange the sensors symmetrically to the width of the liquid container, but at different heights. Provided that the geometry of the sensor arrangement is known, it is also possible to determine the inclination of the motor vehicle using a sensor arrangement of differing heights just mentioned.
If the slope gradient is to be determined only transversely to the direction of travel, the pressure sensor should ideally be mounted symmetrically to the length of the liquid container. In an advantageous embodiment, the present invention mounts two pressure sensors in the liquid container on the horizontal center line of the liquid container running transversely to the direction of travel, at a distance from one another. In this manner, inclinations can be determined only transversely to the direction of travel. Thus, measuring influences due to an inclination of the vehicle in the direction of travel are reduced to a minimum. Instead of arranging the pressure sensors on the horizontal center line running transversely to the direction of travel, it would also be possible to arrange the sensors symmetrically to the length of the liquid container, but at different heights. Provided that the geometry of the sensor arrangement is known, it is also possible to determine the inclination of the motor vehicle using a sensor arrangement of that kind.
In these two embodiments described above, the values of the pressure quantities measured by the two pressure sensors are evaluated in the evaluation unit to determine the roadway gradient quantity. This procedure corresponds to an absolute measurement, since, to determine the roadway gradient quantity, the absolute pressure quantity values are required. In this case, the spatial change of the liquid level is evaluated.
In the above-described embodiments of the present invention having two pressure sensors, the angle of inclination of the liquid surface is independent of the geometry of the liquid container. Also possible is a device for determining the gradient of a roadway surface of a vehicle having four pressure sensors, of which one pair of pressure sensors determines slope gradients in the direction of travel and the other pair determines slope gradients transversely to the direction of travel.
To be able to determine the gradient of the roadway surface both in the direction of travel as well as transversely to the direction of travel, the inclination of the liquid surface relative to the liquid container is determined spatially, i.e., by three measuring points. Using three measuring points, it is possible to ascertain the position of a plane arbitrarily defined in the space. For this reason, the present invention proposes according to another advantageous embodiment to mount three pressure sensors in the liquid container at a distance from one another. Preferably, the pressure sensors are staggered.
Advantageously, the roadway gradient quantity is fed to at least one of an engine timing control, an automatic transmission control, a drive dynamics control, and a unit for detecting mass. To this end, an appropriate arrangement for transmitting the roadway gradient quantity to at least one of an engine timing control, an automatic transmission control, a vehicle dynamics control, or a unit for detecting mass are provided. In this manner, the engine timing, automatic transmission control, drive dynamics control, or the unit for detecting mass can be decisively improved by the additional information of the roadway gradient quantity.
The device according to the present invention can also be expediently used for ascertaining the liquid quantity in the liquid container. In containers without level monitoring, a display of the liquid quantity in the container becomes possible without additional technical effort. In containers which were already provided with an arrangement for level monitoring, this function can be assumed by the device according to the present invention.
A further object is to provide a method for determining a roadway gradient quantity which is executed in the device according to the present invention.